This invention relates to a device and a system for delivering contrast medium to a patient. The device and system are especially effective for delivering carbon dioxide gas to the vascular system of a patient. This invention also relates to an associated method for delivering contrast medium such as carbon dioxide gas to a patient.
Delivery systems for contrast media have been used for many years in the medical field. Keeping the system a "closed system" so that no room air will be introduced is critical to the features of these delivery systems. With the advent of carbon dioxide gas or CO.sub.2 as a viable fluid for displacing blood in vessels for visualization under Digital Subtraction Angiography (DSA), the need to keep air out of the system is of even greater importance. Air and CO.sub.2 are invisible so introduction of air into a CO.sub.2 delivery system would pose a danger to a patient if it were inadvertently injected into the vasculature.
CO.sub.2 has been shown to be an excellent fluid to be used for displacing blood in vessels. This void that is created in the vessel can be visualized with DSA. But since CO.sub.2 is invisible introduction of room air into the system would pose a great danger to the patient. The air would go undetected and, once in the patient's vasculature, could cause a blockage or even an air embolism to the brain resulting in a stroke or death.
Because of this serious safety issue, it would make sense to use a closed system for the safe delivery of CO.sub.2. However, the conventional method used for delivering CO.sub.2 is connecting a syringe to a CO.sub.2 cylinder, filling the syringe with CO.sub.2, disconnecting the syringe from the cylinder and re-connecting to a catheter or tube set. If more CO.sub.2 is needed, the syringe is disconnected from the catheter and refilled of the cylinder. This method allows for introduction of air into the system at every disconnection.
One method that was developed to reduce the number of disconnections was to attach the CO.sub.2 cylinder directly to a stopcock with a syringe attached at on port and the catheter to the patient attached to the other port. When the syringe was to be filled, the stopcock would be opened to the syringe and the cylinder pressure would force CO.sub.2 into the syringe. For injection into the patient, the stopcock would be closed to the cylinder and the syringe plunger would be advanced forward pushing the CO2 gas into the catheter and, subsequently, into the patient.
The problem with this method is that the CO.sub.2 cylinder pressure is much higher than blood pressure (830 psi vs. 6 psi). If the stopcock is turned the wrong way, the cylinder is open to the catheter and liters of CO.sub.2 will be delivered into the patient in less than a minute. Accordingly, the cylinder must be isolated from the patient and the delivery system used must be closed without providing a chance for the introduction of air.